Chimeric canine anti-CD20 antibody

ABSTRACT

The disclosure relates to caninized chimeric anti-CD20 antibodies to the canine protein CD20 and methods of use to treat certain disorders such as non-Hodgkins B-cell lymphoma in dogs.

This application claims priority to PCT Application Number PCT/US2017/017337, filed Feb. 10, 2017 and published in English as WO2017/142800 on Aug. 24, 2017, which claims priority to U.S. Provisional Application No. 62/296,729 filed Feb. 18, 2016.

The instant application contains a Sequence Listing which has been submitted electronically in ASCII format and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Feb. 10, 2016 and re-created on Nov. 2, 2018, is named “X20914 sequence listing” and is 14 Kb in size.

The present invention relates to caninized chimeric anti-CD20 antibodies to the canine protein CD20 and methods of use to treat certain disorders such as non-Hodgkins B-cell lymphoma in dogs.

The present invention is in the field of treatment of cancer.

Canine lymphomas are a diverse group of cancers, and are among the most common cancers diagnosed in dogs. They collectively represent approximately 7-14% of all cancers diagnosed in dogs. There are over 30 described types of canine lymphoma, and these cancers vary tremendously in their behavior. Some progress rapidly and are acutely life-threatening without treatment, while others progress very slowly and are managed as chronic, indolent diseases. Lymphomas may affect any organ in the body, but most commonly originate in lymph nodes, before spreading to other organs such as the spleen, liver, and bone marrow.

CD20 is a cell-surface protein with four transmembrane spanning regions. The CD20 molecule is involved in regulation of B-cell proliferation and differentiation. The CD20 antigen is present exclusively on the surface of almost all B-cells, both normal and malignant.

Rituximab is a chimeric monoclonal antibody against the human protein CD20 which is primarily found on the surface of immune system B-cells. Rituximab destroys B-cells and is therefore used to treat diseases in humans which are characterized by excessive numbers of B-cells, overactive B-cells, or dysfunctional B-cells. This includes many lymphomas, leukemias, transplant rejection, and autoimmune disorders.

Rituximab destroys both normal and malignant human B-cells that have CD20 on their surfaces. The effect results in the elimination of B-cells (including the cancerous ones) from the body, allowing a new population of healthy B-cells to develop from lymphoid stem cells.

Unfortunately, a cure for canine lymphomas still remains elusive and there exists a need for more and different therapies that may prove to be effective in treating them.

K9LO-133 is a chimeric anti-CD20 antibody that targets mature B-lymphocytes in dogs. K9LO-133 binds to CD20 on canine B-lymphocytes. K9LO-133 is potentially useful for treatment for non-Hodgkins B cell lymphoma and other types of lymphoma in dogs.

Accordingly, the present invention provides an antibody that specifically binds to canine CD20. The present invention also provides a method of treating lymphoma in a canine patient by administering to a lymphoma cancer canine patient in need of such treatment an effective amount of an antibody that specifically binds to canine CD20. The present invention provides for a pharmaceutical composition including an antibody that specifically binds to canine CD20, and one or more pharmaceutically acceptable carriers, diluents, or excipients. The present invention also provides an antibody that specifically binds to canine CD20 and also binds to protein A.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 depicts the serum levels of B-lymphocytes CD21+ and CD22+ and T-lymphocytes CD4+ and CD8+ from −5 to 37 days in dogs treated with K9LO-133 antibody.

DETAILED DESCRIPTION

Unless indicated otherwise, the term “antibody” (Ab) refers to an immunoglobulin molecule comprising two heavy chains (HC) and two light chains (LC) interconnected by disulfide bonds. The amino terminal portion of each chain includes a variable region of about 100 to about 110 amino acids primarily responsible for antigen recognition via the complementarity determining regions (CDRs) contained therein. The carboxy-terminal portion of each chain defines a constant region primarily responsible for effector function.

As used herein, the term “antigen-binding fragment” refers to any antibody fragment that retains the ability to bind to its antigen. Such “antigen-binding fragments” can be selected from the group consisting of Fv, scFv, Fab, F(ab′)₂, Fab′, scFv-Fc fragments and diabodies. An antigen-binding fragment of an antibody will typically comprise at least one variable region. Preferably, an antigen-binding fragment comprises a heavy chain variable region (HCVR) and a light chain variable region (LCVR). More preferably, an antigen-binding fragment as used herein comprises a HCVR and a LCVR which confers antigen-binding specificity to canine CD20 (i.e., a “canine CD20 binding fragment”).

As used herein, the terms “complementarity determining region” and “CDR”, refer to the non-contiguous antigen combining sites found within the variable region of LC and HC polypeptides of an antibody or an antigen-binding fragment thereof. These particular regions have been described by others including Kabat, et al., Ann. NY Acad. Sci. 190:382-93 (1971); Kabat et al., J. Biol. Chem. 252:6609-6616 (1977); Kabat, et al, Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242 (1991); Chothia, et al., J. Mol. Biol. 196:901-917 (1987); MacCallum, et al., J. Mol. Biol., 262:732-745 (1996); and North, et al., J. Mol. Biol., 406, 228-256 (2011), where the definitions include overlapping or subsets of amino acid residues when compared against each other.

As used herein, the term “light chain variable region” refers to a portion of a LC of an antibody molecule that includes amino acid sequences of Complementarity Determining Regions (CDRs; i.e., LCDR1, LCDR2, and LCDR3), and Light Framework Regions (LFRWs).

As used herein, the term “heavy chain variable region (HCVR)” refers to a portion of a HC of an antibody molecule that includes amino acid sequences of Complementarity Determining Regions (CDRs; i.e., HCDR1, HCDR2, and HCDR3), and Heavy Framework Regions (HFRWs).

The CDRs are interspersed with regions that are more conserved, termed framework regions (“FRW”). Each LCVR and HCVR is composed of three CDRs and four FRWs, arranged from amino-terminus to carboxy-terminus in the following order: FRW1, CDR1, FRW2, CDR2, FRW3, CDR3, FRW4. The three CDRs of the light chain are referred to as “LCDR1, LCDR2, and LCDR3” and the three CDRs of the HC are referred to as “HCDR1, HCDR2, and HCDR3.” The CDRs contain most of the residues which form specific interactions with the antigen. The numbering and positioning of CDR amino acid residues within the LCVR and HCVR regions is in accordance with known conventions (e.g., Kabat (1991), Chothia (1987), and/or North (2011)). In different embodiments of the invention, the FRWs of the antibody may be identical to the germline sequences, or may be naturally or artificially modified.

In certain embodiments, the anti-CD20 Ab for the methods and/or uses of the present invention is altered to increase or decrease the extent to which the antibody is glycosylated. Addition or deletion of glycosylation sites to an antibody may be conveniently accomplished by altering the amino acid sequence such that one or more glycosylation sites is created or removed.

Unless indicated otherwise, when referring to an amino acid residue in an antibody by a number, the EU numbering system is used herein as it is conventionally used in the art (see, Kabat, et al., Sequences of Proteins of Immunological Interest, Fifth Edition, U.S. Department of Health and Human Services, NIH Publication No. 91-3242 (1991), for example).

As used herein, the term “kit” refers to a package comprising at least two separate containers, wherein a first container contains a K9LO-133 Ab and a second container contains pharmaceutically acceptable carriers, diluents, or excipients. As used herein, the term “kit” also refers to a package comprising at least two separate containers, wherein a first container contains K9LO-133 Ab, and another antibody preferably for the treatment of cancers other than lymphomas. A “kit” may also include instructions to administer all or a portion of the contents of these first and second containers to a cancer patient. Optionally, these kits also include a third container containing a composition comprising a known chemotherapeutic agent.

As used herein, the terms “treating,” “to treat,” or “treatment” refers to restraining, slowing, stopping, reducing, or reversing the progression or severity of an existing symptom, disorder, condition, or disease.

As used herein, the term “effective amount” refers to the amount or dose of a caninized anti-CD20 Ab which, upon single or multiple dose administration to the patient, provides an effective response in the patient under diagnosis or treatment.

As used herein, the terms “effective response” of a patient or a patient's “responsiveness” to treatment with a combination of agents, or “therapeutic effect” refers to the clinical or therapeutic benefit(s) imparted to a patient upon administration of a caninized anti-CD20 Ab. Such benefit(s) include any one or more of: extending survival (including overall survival and progression free survival); resulting in an objective response (including a complete response or a partial response); decreasing amount of B-cells, decreasing concentration of B-cells in a patient's blood or other tissues and fluids, tumor regression, tumor weight or size shrinkage, longer time to disease progression, increased duration of survival, longer progression free survival, improved overall response rate, increased duration of response, and improved quality of life and/or improving signs or symptoms of cancer, etc.

An effective amount can be readily determined by the attending diagnostician, as one skilled in the art, by the use of known techniques and by observing results obtained under analogous circumstances. In determining the effective amount for a patient, a number of factors are considered by the attending diagnostician, including, but not limited to: the species or breed of patient; its size, age, and general health; the specific disease or disorder involved; the degree of or involvement or the severity of the disease or disorder; the response of the individual patient; the particular compound administered; the mode of administration; the bioavailability characteristics of the preparation administered; the dose regimen selected; the use of concomitant medication; and other relevant circumstances.

K9LO-133

AME-133V is a second generation humanized IgG1 monoclonal antibody. K9LO-133 is a partially caninized (human variable regions with canine constant regions) isotype C monoclonal antibody version of AME-133V that specifically binds to CD20 protein in dogs.

In an embodiment, K9LO-133 contains engineered variable regions of the heavy and light chains, CDRs and frameworks. In an embodiment, a residue variant in LCDR1 of K9LO-133 is introduced. In an embodiment, the residue variant in LCDR1 of K9LO-133 is V165G. In an embodiment, a variant hinge region is introduced. In an embodiment, a variant region downstream of the hinge is added. In an embodiment, the variant region downstream of the hinge allows K9LO-133 to bind to protein A.

K9LO-133 has a heavy chain amino acid sequence corresponding to SEQ ID NO: 1 and a corresponding nucleotide sequence SEQ ID NO: 2 that encodes for the amino acid of SEQ ID NO: 1. K9LO-133 has a heavy chain variable region sequence of SEQ ID NO: 3. The heavy chain variable sequence region further consists of HFWK 1 (SEQ ID NO: 4), HCDR1 (SEQ ID NO: 5), HFWK 2 (SEQ ID NO: 6), HCDR2 (SEQ ID NO: 7), HFWK3 (SEQ ID NO: 8), and HCDR3 (SEQ ID NO: 9).

K9LO-133 has a light chain amino acid sequence corresponding to SEQ ID NO: 10 and a corresponding nucleotide sequence SEQ ID NO: 11 that encodes for the amino acid of SEQ ID NO: 10. K9LO-133 has a light chain variable region sequence of SEQ ID NO: 12. The light chain variable sequence region further consists of LFWK 1 (SEQ ID NO: 13), LCDR1 (SEQ ID NO: 14), LFWK 2 (SEQ ID NO: 15), LCDR2 (SEQ ID NO: 16), LFWK 3 (SEQ ID NO: 17), LCDR3 (SEQ ID NO: 18), and a J region (SEQ ID NO: 19).

CD20 Expression in Canine Lymphoma Tissue

CD20 expression in canine lymphoma tissue can be evaluated using immunohistochemistry (IHC) with AME-133V and K9LO-133. In order to detect binding, AME-133V and K9LO-133 can be applied to cryosections of canine lymphoma samples at one concentration, for example 10 μg/mL. In addition, AME-133V and K9LO-133 can be substituted with an appropriate species and isotype matched negative control antibody which has a different antigenic specificity from that of detection antibodies, for example, either human IgG1, designated HuIgG1, (for AME-133V) and dog IgG, designated DgIgG (for K9LO-133). Other controls can be produced by omission of the detection antibodies or negative control antibodies from the assay (assay control).

When tested essentially as described above, AME-133V and K9LO-133 produced 3+ staining of >75% of the positive control mononuclear leucocytes. For K9LO-133, 3+ staining was observed in lymphocytes in the white pulp in canine spleen. AME-133V and K9LO-133 did not specifically react with the negative control smooth myocytes (specifically nuclei for K9LO-133) in canine spleen. The negative control antibodies, HuIgG and DgIgG, did not specifically react with either the positive or negative control tissue elements in canine spleen. There also was no staining of the assay control slides. The specific reactions of AME-133V and K9LO-133 with the positive control tissue element and the lack of specific reactivity with the negative control tissue element, as well as the lack of reactivity of the negative control antibody, indicated that the assay was sensitive, specific, and reproducible.

CD20 was detected in >75% of the neoplastic cells in 8 of 10 canine lymphoma samples examined. In the other samples, 1-5% of neoplastic cells were positively stained for CD20.

K9LO-133 Treated Dogs

The human dose for Rituximab for the treatment of non-Hodgkin's lymphoma is 375 mg/m². Generally, a canine chemotherapeutic dose is 40% of a human dose, irrespective of cancer type. Therefore, and without being bound by theory, an appropriate starting dose of an anti-CD20 antibody for canine non-Hodgkin's lymphoma is about 150 mg/m². In order to adjust for body surface area of a 7 kg dog, the 150 mg/m² number was corrected by multiplying by 0.37. The resulting dose of K9LO-133 administered to the dogs was about 57 mg/dog.

In an embodiment, the dose of K9LO-133 administered to a dog is from about 140 mg to about 160 mg per meter squared of body surface area. In an embodiment, the dose of K9LO-133 administered to a dog is from about 130 mg to about 170 mg per meter squared of body surface area. In an embodiment, the dose of K9LO-133 administered to a dog is from about 110 mg to about 190 mg per meter squared of body surface area. In an embodiment, the dose of K9LO-133 administered to a dog is from about 50 mg to about 250 mg per meter squared of body surface area.

In an embodiment, the dose of K9LO-133 administered to a dog is from about 50 mg/dog to about 60 mg/dog. In another embodiment, the dose of K9LO-133 administered to a dog is from about 40 mg/dog to about 70 mg/dog. In an embodiment, the dose of K9LO-133 administered to a dog is from about 30 mg/dog to about 100 mg/dog. In an embodiment, the dose of K9LO-133 administered to a dog is from about 10 mg/dog to about 1000 mg/dog.

The efficacy of K9LO-133 was determined in dogs by dosing them intravenously (IV) at about 150 mg/m² on Days 0, 7, and 35. Three female Beagle dogs were acclimated to study conditions for seven days during which they were subjected to physical examinations; body weight measurements; and daily clinical observations. On dosing days, dogs were dosed with 57 mg of K9LO-133 via slow IV infusion at a rate of 0.5 to 1 mL/min.

Blood was collected for determination of lymphocyte proportions and serum retention on Days −5, 2, 9, 16, 23, 30, and 37.

As depicted in FIG. 1, there was a drop in the proportion of blood B-lymphocytes after treatment with K9LO-133. The proportion of B-lymphocytes (CD21+ and CD22+) dropped on Day 2, showed a recovery between Days 2 and 30, but had not yet returned to baseline levels by Day 37. CD8+T-lymphocytes showed a decrease on Day 16 but had returned to baseline levels by Day 23. The proportion of CD4+T-lymphocytes remained relatively constant.

Thus, IV administration of K9LO-133 reduced B-lymphocyte counts in circulation with a transient decrease in CD8+T-lymphocytes in treated dogs.

In an aspect, disclosed herein is an antibody having a light chain variable region (LCVR) whose amino acid sequence is that given in SEQ ID NO: 12, and a heavy chain variable region (HCVR) whose amino acid sequence is that given in SEQ ID NO: 3. In an embodiment, the antibody specifically binds to canine CD20.

In another aspect, disclosed herein is an antibody having a light chain (LC) whose amino acid sequence is that given in SEQ ID NO: 10, and a heavy chain (HC) whose amino acid sequence is that given in SEQ ID NO: 1 is disclosed. In an embodiment, the antibody specifically binds to canine CD20.

In an aspect, disclosed herein is an antibody having two light chains (LC) each having an amino acid sequence that is given in SEQ ID NO: 10, and two heavy chains (HC) each having an amino acid sequence that is given in SEQ ID NO: 1. In an embodiment, the antibody specifically binds to canine CD20.

In another aspect, a method of treating lymphoma in a canine patient is disclosed that includes administering to a lymphoma cancer canine patient in need of such treatment an effective amount of an antibody having a light chain variable region (LCVR) whose amino acid sequence is that given in SEQ ID NO: 12, and a heavy chain variable region (HCVR) whose amino acid sequence is that given in SEQ ID NO: 3, and the antibody specifically binds to canine CD20. In an embodiment, the antibody has a light chain (LC) whose amino acid sequence is that given in SEQ ID NO: 10, and a heavy chain (HC) whose amino acid sequence is that given in SEQ ID NO: 1. In an embodiment, the antibody is K9LO-133.

In an aspect, a kit is disclosed that has a pharmaceutical composition containing K9LO-133 with one or more pharmaceutically acceptable carriers, diluents, or excipients.

In another aspect, an antibody is disclosed having a light chain (LC) whose amino acid sequence is that given in SEQ ID NO: 10, and a heavy chain (HC) whose amino acid sequence is that given in SEQ ID NO: 1, and the antibody specifically binds to canine CD20, and the antibody binds to protein A.

EXAMPLES

K9LO-133

K9LO-133 can be supplied in 10 mM citrate, 150 mM NaCl, pH 6.5 at 26.3 mg/mL. The vehicle can be physiological saline at 0.9% NaCl.

Dosing of K9LO-133 can be based on body surface area, which was estimated for the dogs in this study to be 0.37 m². Each dog received 150 mg/m² (57 mg) of K9LO-133 at each dose. Doses were prepared by drawing up 57 mg (2.2 mL) of K9LO-133 and diluting in 27.8 mL of physiologic saline to bring the total volume to 30 mL for infusion.

Flow Cytometry

T-lymphocyte (CD4+ and CD8+) and B-lymphocyte (CD21+ and CD22+) amounts can be determined by flow cytometry. Blood collection for flow cytometry was performed prior to feeding. Approximately 1 mL of EDTA anti-coagulated blood was provided from 3 dogs at baseline (day −5), and on Days 2, 9, 16, 23, 30 and 37. Red blood cells were lysed with ammonium chloride hypotonic buffer, and leukocytes were stained with antibodies reactive with canine CD4, CD8, CD21 and CD22. Then, unbound antibodies were removed and the acquisition of 10,000 leukocyte events in a FACScan or a FACSAria flow cytometer were obtained.

Lymphoma Samples

Ten frozen canine lymphoma samples were trimmed and embedded in Tissue-Tek® OCT (Optimal Cutting Temperature) compound and stored in a freezer set to maintain −80° C. until sectioning. Sections were cut at approximately 5 μm to generate an appropriate number of slides for subsequent IHC staining.

Immunohistochemistry Staining

Sections from each lymphoma sample were stained using AME-133V, a human IgG1 monoclonal antibody directed against human CD20, and K9LO-133, a chimeric canine isotype C monoclonal antibody directed against canine CD20, using IHC as detailed below. AME-133V was in a 19.5 mg/mL solution in phosphate-buffered saline (PBS), pH 7.4. K9LO-133 was in a 2.5 mg/mL solution in PBS, pH 7.4.

IHC staining was performed including use of positive and negative control materials in each staining run and using additional slides for the negative control antibody and assay control to ensure stain specificity. The staining procedures, primary and secondary antibody dilutions, and controls for AME-133V were qualified in preliminary staining runs. The staining procedures, primary and secondary antibody dilutions, and controls for K9LO-133 were qualified in a methods development staining run.

AME-133V Staining

The indirect immunoperoxidase procedure can be used to stain the canine lymphoma tissue with AME-133V to detect CD20. Slides were fixed in acetone for 10 minutes at room temperature at the time of sectioning. Acetone-fixed cryosections were rinsed twice in phosphate-buffered saline, 0.15 M NaCl, pH 7.2 PBS. Endogenous peroxidase was then quenched by incubation of the slides with Biocare PeroxAbolish for 5 minutes at room temperature. Next, the slides were rinsed twice with PBS, incubated with the avidin solution for 15 minutes, rinsed once with PBS, incubated with the biotin solution for 15 minutes, and rinsed once with PBS. The slides were then treated with a protein block designed to reduce nonspecific binding for 20 minutes. The protein block was prepared as follows: PBS+1% bovine serum albumin (BSA); 0.5% casein; and 3% donkey serum.

Following the protein block, the primary antibodies AME-133V, Human IgG1, or none were applied to the slides at a concentration of 10 μg/mL for 1 hour. Then, the slides were rinsed twice with PBS, and the biotinylated secondary antibody (donkey anti-human IgG) was applied to the slides for 30 minutes. Next, the slides were rinsed twice with PBS, reacted for 30 minutes with the ABC Elite reagent, and rinsed twice with PBS. Next, DAB was applied for 4 minutes as a substrate for the peroxidase reaction. All slides were rinsed with tap water, counterstained, dehydrated, and mounted. PBS+1% BSA served as the diluent for primary antibodies and ABC Elite reagent. (PBS+1% BSA)+canine IgG (1:25 dilution) served as the diluent for the secondary antibody.

K9LO-133 Staining

The indirect immunoperoxidase procedure can be used to stain the canine lymphoma tissue with K9LO-133 to detect CD20. The requirement for labeling (e.g. biotin, peroxidase, or fluorescein) of K9LO-133 and preclusion of nonspecific reactivity between the secondary labeled anti-canine IgG and IgG endogenous to the tissues examined can be eliminated according to the following process. The labeled secondary antibody was allowed to attach specifically to the unlabeled primary antibody (K9LO-133, DgIgG, or none) by overnight incubation of the primary/secondary antibody mixtures prior to application to the tissue cryosections. The detection reagent or negative control antibody (at a concentration of 10 μg/mL) was mixed with biotinylated rabbit anti-dog IgG, Fc fragment-specific antibody (RbαDgIgG) at a concentration of 15 μg/mL to achieve a primary:secondary antibody ratio of 1:1.5 on the day prior to staining.

Precomplexed antibodies were incubated overnight on a rocker mechanism in a refrigerator set to maintain 4° C. Prior to use of the antibody on the subsequent day, dog gamma globulins were added to each vial to achieve a final concentration of 3 mg/mL, and then incubated for at least 2 hours on the rocker mechanism in a refrigerator set to maintain 4° C. Slides were fixed in acetone for 10 minutes at room temperature at the time of sectioning. On the day of staining, the slides were rinsed twice with Tris-buffered saline, 0.15M NaCl, pH 7.6 TBS. Endogenous peroxidase was then quenched by incubation of the slides with an appropriate reagent such as Biocare PeroxAbolish reagent for 5 minutes at room temperature. Next, the slides were rinsed twice with TBS, incubated with the avidin solution for 15 minutes, rinsed once with TBS, incubated with the biotin solution for 15 minutes, and rinsed once with TBS. The slides were then treated with a protein block designed to reduce nonspecific binding for 20 minutes.

The protein block was prepared as follows: TBS+1% bovine serum albumin (BSA), 0.5% casein; and 3% normal rabbit serum. Following the protein block, the precomplexed primary and secondary antibodies were applied to the slides for two hours. Next, the slides were rinsed twice with TBS, treated with the ABC Elite reagent for 30 minutes, rinsed twice with TBS, and then treated with DAB for 4 minutes as a substrate for the peroxidase reaction. All slides were rinsed with tap water, counterstained, dehydrated, and mounted. TBS+1% BSA served as the diluent for all antibodies and ABC reagent. Each staining run included a positive control (mononuclear leucocytes), and a negative control (smooth myocytes) of cryosections of canine spleen.

SEQUENCE LISTING SEQ ID NO: 1; PRT; Artificial Sequence EVQLVQSGAEVKKPGESLKISCKGSGRTFTSYNMHWVRQMPGKGLEW MGAIYPLTGDTSYNQKSKLQVTISADKSISTAYLQWSSLKASDTAMY YCARSTYVGGDWQFDVWGKGTTVTVSSASTTAPSVFPLAPSCGSQSG STVALACLVSGYIPEPVTVSWNSGSLTSGVHTFPSVLQSSGLYSLSS MVTVPSSRWPSETFTCNVAHPATNTKVDKPVPKRENGRVPRPPDCPK CPAPELLGGPSVFIFPPKPKDTLLIARTPEVTCVVVDLDPENPEVQI SWFVDSKQVQTANTQPREEQSNGTYRVVSVLPIGHQDWLSGKQFKCK VNNKALPSPIEEIISKTPGQAHQPNVYVLPPSRDEMSKNTVTLTCLV KDFFPPEIDVEWQSNGQQEPESKYRMTPPQLDEDGSYFLYSKLSVDK SRWQRGDTFICAVMHEALHNHYTQISLSHSPGK SEQ ID NO: 2; DNA; Artificial Sequence GAGGTGCAGCTCGTGCAGTCTGGACCAGAGGTGAAAAAGCGCGGGGA GTCTCTGAAGATCTCCTGTAAGGGTTCTGGCCGTACATTTACCAGTT ACAATATGCACTGGGTGCGCCAGATGCCCGGGAAAGGCCTGGAGTGG ATGGGGGCTATTTATCCCTTGACGGGTGATACTTCCTACAATCAGAA GTCGAAACTCCAGGTCACCATCTCAGCCGACAAGTCCATCAGCACCG CCTACCTGCAGTGGAGCAGCCTGAAGGCCTCGGACACCGCCATGTAT TACTGTGCGAGATCGACTTACGTGGGCGGTGACTGGCAGTTCGATGT CTGGGGCAAGGGGACCACGGTCACCGTCTCCTCAGCCTCCACCACGG CCCCCTCGGTTTTCCCGCTAGCGCCCAGCTGTGGGTCCCAATCCGGC TCCACGGTGGCCCTGGCCTGCCTGGTGTGAGGCTACATGCCCGAGCG TGTAACTGTGTCGTGGAATTCCGGCTCCTTGACCAGCGGTGTGCACA CCTTCCCGTCCGTCCTGCAGTCCTCAGGGCTCTACTCCCTCAGCAGC ATGGTGACAGTGCCCTCCAGCAGGTGGCCCAGCGAGACCTTCACCTG CAATGTGGCCCACCCGGGCACCAACACTAAAGTAGACAAGCCAGTGC CCAAAAGAGAAAATGGAAGAGTTCCTCGCCCACCTGATTGTCCCAAA TGCCCAGCCCCTGAACTGCTGGGAGGGCCTTCGGTCTTCATCTTTCC CCCAAAACCCAAGGACACCCTCTTGATTGCCCGAACACCTGAGGTCA CATGTGTGGTGGTGGATCTGGACCCAGAAAACCCTGAGGTGCAGATC AGCTGGTTCGTGGATAGTAAGCAGGTGCAAACAGCCAACACGCAGCC TCGTGAGGAGCAGTCCAATGGCACCTACCGTGTGGTCAGTGTCCTCC CCATTGGGCACCAGGACTGGCTTTCAGGGAAGCAGTTCAAGTGCAAA GTCAACAACAAAGCCCTCCCATCCCCCATTGAGGAGATCATCTCCAA GACCCCAGGGCAGGCCCATCAGCCTAATGTGTATGTCCTGCCGCCAT CGCGGGATGAGATGAGCAAGAATACGGTCACCCTGACCTGTCTGGTC AAAGACTTCTTCCCACCTGAGATTGATGTGGAGTGGCAGAGCAATGG ACAGCAGGAGCCTGAGAGCAAGTACCGCATGAGCGCGCCCCAGCTGG ATGAAGATGGGTGCTACTTCCTATACAGCAAGCTCTCCGTGGACAAG AGCCGCTGGCAGCGGGGAGACACCTTCATATGTGCGGTGATGCATGA AGCTCTACACAACCACTACACACAGATATCCCTCTCCCATTCTCCGG GTAAATGATGATAG SEQ ID NO: 3; PRT; Artificial Sequence EVQLVQSGAEVKKPGESLKISCKGSGRTFTSYNMHWVRQMPGKGLEW MGAIYPLTGDISYNQKSKLQVTISADKSISTAYLQWSSLKASDTAMY YCARSTYVGGDWQFDVWGKGTTVTVSS SEQ ID NO: 4; PRT; Artificial Sequence EVQLVQSGAEVKKPGESLKISC SEQ ID NO: 5; PRT; Artificial Sequence KGSGRTFTSYNMH SEQ ID NO: 6; PRT; Artificial Sequence WVRQMPGKGLEWMG SEQ ID NO: 7; PRT; Artificial Sequence AIYPLTGDTSYNQKSKL SEQ ID NO: 8; PRT; Artificial Sequence QVTISADKSISTAYLQWSSLKASDTAMYYC SEQ ID NO: 9; PRT; Artificial Sequence ARSTYVGGDWQFDV SEQ ID NO: 10; PRT; Artificial Sequence EIVLTQSPGTLSLSPGERATLSCRASRSVPYIHWYQQKPGQAPRLLI YATSALASGIPDRFSGSGSGTDFTLTISRLEPEDFAVYYCQQWLSNP PTFGQGTKLEIKRNDAQPAVYLFQPSPDQLHTGSASVVCLLNSFYPK DINVKWKVDGVIQDTGIQESVTEQDKDSTYSLSSTLTMSSTEYLSHE LYSCEITHKSLPSTLIKSFQRSECQRVD SEQ ID NO: 11; DNA; Artificial Sequence GAAATTGTGTTGACGCAGTCTCCAGGCACCCTGTCTTTGTCTCCAGG GGAAAGAGCCACCCTCTCCTGCAGGGCCAGCCGGAGTGTACCGTACA TCCACTGGTACCAGCAGAAACCTGGCCAGGCTCCCAGGCTCCTCATC TATGCCACATCCGCTCTGGCTTCTGGCATCCCAGACAGGTTCAGTGG CAGTGGGTCTGGGACAGACTTCACTCTCACCATCAGCAGACTGGAGC CTGAAGATTTTGCAGTGTATTACTCTCAGCAGTGGCTGAGTAACCCA CCCACTTTTGGCCAGGGGACCAAGCTGGAGATCAAACGAAATGATGC CCAGCCAGCCGTCTATTTGTTCCAACCATCTCCAGACCAGTTACACA CAGGAAGTGCCTCTGTTGTGTGCTTGCTGAATAGCTTCTAGCCGAAA GACATCAATGTCAAGTGGAAAGTGGATGGTGTCATCCAAGACACAGG CATCCAGGAAAGTGTCACAGAGCAGGACAAGGACAGTACCTACAGCC TCAGCAGCACCCTGACGATGTCCAGTACTGAGTACCTAAGTCATGAG TTGTACTCCTGTGAGATCACTCACAAGAGCCTGCCCTCCACCCTCAT CAAGAGCTTCCAAAGGAGCGAGTGTCAGAGAGTGGAC SEQ ID NO: 12; PRT; Artificial Sequence EIVLTQSPGTLSLSPGERATLSCRASRSVPYIHWYQQKPGQAPRLLI YATSALASGIPDRFSGSGSGTDFTLTISRLEPEDFAVYYCQQWLSNP PTFGQGTKLEIK SEQ ID NO: 13; PRT; Artificial Sequence EIVLTQSPGTLSLSPGERATLSC SEQ ID NO: 14; PRT; Artificial Sequence RASRSVPYIH SEQ ID NO: 15; PRT; Artificial Sequence WYQQKPGQAPRLLI SEQ ID NO: 16; PRT; Artificial Sequence YATSALAS SEQ ID NO: 17; PRT; Artificial Sequence GIPDRFSGSGSGTDFTLTISRLEPEDFAVYYC SEQ ID NO: 18; PRT; Artificial Sequence QQWLSNPPT SEQ ID NO: 19; PRT; Artificial Sequence FGQGTKLEIK 

What is claimed is:
 1. An antibody comprising a light chain variable region (LCVR) whose amino acid sequence is that given in SEQ ID NO: 12, and a heavy chain variable region (HCVR) whose amino acid sequence is that given in SEQ ID NO:
 3. 2. The antibody of claim 1, wherein the antibody specifically binds to canine CD20.
 3. The antibody of claim 1, wherein the antibody comprises a light chain (LC) whose amino acid sequence is that given in SEQ ID NO: 10, and a heavy chain (HC) whose amino acid sequence is that given in SEQ ID NO:
 1. 4. The antibody of claim 3, wherein the antibody specifically binds to canine CD20.
 5. The antibody of claim 1, wherein the antibody comprises two light chains (LC) each having an amino acid sequence that is given in SEQ ID NO: 10, and two heavy chains (HC) each having an amino acid sequence that is given in SEQ ID NO:
 1. 6. The antibody of claim 5, wherein the antibody specifically binds to canine CD20.
 7. A method of treating lymphoma in a canine patient, comprising administering to a lymphoma cancer canine patient in need of such treatment an effective amount of an antibody comprising a light chain variable region (LCVR) whose amino acid sequence is that given in SEQ ID NO: 12, and a heavy chain variable region (HCVR) whose amino acid sequence is that given in SEQ ID NO: 3, wherein the antibody specifically binds to canine CD20.
 8. The method according to claim 7 wherein the antibody comprises a light chain (LC) whose amino acid sequence is that given in SEQ ID NO: 10, and a heavy chain (HC) whose amino acid sequence is that given in SEQ ID NO:
 1. 9. A kit, comprising a pharmaceutical composition, comprising an antibody which specifically binds to canine CD20, with one or more pharmaceutically acceptable carriers, diluents, or excipients; wherein the antibody which specifically binds to canine CD20 comprises a light chain variable region (LCVR) whose amino acid sequence is that given in SEQ ID NO: 12, and a heavy chain variable region (HCVR) whose amino acid sequence is that given in SEQ ID NO:
 3. 10. The antibody of claim 4, wherein the antibody binds to protein A. 